crow is not a DC coupled audio interface. There are ways to communicate CV between crow and a computer but you cannot stream audio from your PC to crow or vice versa, it’s not designed for that – all USB communication with crow is basically done as text, and at a lower speed than is used by USB audio.
I have not used an ES-8 but my impression is that it has basically a fixed function, namely acting as an analog/digital interface for directly passing signals through. By contrast crow’s functionality is completely user-defined: you can have crow generate LFOs, sequences, envelopes, etc. on its own, or quantize incoming voltages, or perform any number of unique CV processing functions. Since crow is scriptable it can serve many different use cases and can be a powerful way to experiment with live coding that’s well integrated in a modular system. There are also a lot of Max and M4L options for interacting with crow as a CV interface and this is one of the main areas of crow development, I’m not well versed in Max but you can find some details here. I would say they are devices with fairly different design goals / supported signals / interaction schemes.
As far as interacting with norns, crow can be incorporated into norns scripts as a CV input or output interface, and a lot of norns scripts support some kind of crow interaction modes (or if not it can be easy to add one). To my knowledge no one is actually using ES-8 with norns currently (?) – norns expects to use its own sound I/O, JACK is not really designed for using multiple audio devices concurrently, this thread discusses what would be involved in configuring ES-8 as an alternative audio device.
